RE: A metal part came out of my Hacker A60-7XS motor - advice.
If you want to remove the bell, it looks like all you need to do is to remove the hex screw from the back end of the shaft. Then the bell will come out (but the magnets will resist, be careful). So no grub screws or clips in this motor, just like the O.S. brushless.
To me that part looks like it doesn't even belong in the motor. The washer in the other Hacker looks too different. I'd certainly open the motor and check for any damage inside. Also check that the necessary washers are in place. I suppose they are if there is no extra play.